Technologies relating to systems and methods for manipulating minute volumes of fluids, such as biological and chemical fluids, are widely referred to as microfluidics. The realized and potential applications of microfluidics include disease diagnosis, life science research, and biological and/or chemical sensor development.
A microfluidic structure including a substrate having one or more microfluidic channels or pathways and a cover plate or a second or more substrates with fluid pathways that may or may not be interconnected, may commonly be referred to as a microfluidic chip. A highly integrated microfluidic chip is sometimes called a ‘Lab-on-a-chip’. Inorganic microfluidic chips having substrates made of glass, quartz or silicon have advantageous organic solvent compatibilities, high thermal and dimensional stability and excellent feature accuracy. These chips are typically fabricated using well-established microfabrication technologies developed for the semiconductor industry. However, the material and production costs of the inorganic chips may become prohibitively high especially when the fluidic pathway(s) requires significant area or the chip has to be disposable. In addition, many established biological assays were developed utilizing the surface properties of polymeric substrates. The research effort required to redevelop these assays on inorganic surfaces would require significant time and resource investments.
As an alternative to inorganic microfluidic structures such as those referred to immediately above, microfluidic structures or devices can also be made from polymeric materials. Polymeric microfluidic structures have advantageously low material costs and the potential for mass production.
As such, scientists and engineers are growing ever closer to delivering on the promise of inexpensive and fully integrated microfluidic systems. However, there are remaining obstacles. For these systems to be useful and helpful, they must provide the components and structures that are necessary to carry out assays and other operations of interest. These components include pumps, valves, and channels, as well as more complex structures, such as mixing devices and sensors. Although, the materials employed to manufacture microfluidic devices are becoming less expensive, the actual costs of these devices will not become sufficiently low for mass use until the costs of manufacturing these components also decreases.
However, the fabrication of polymeric microfluidic chips presents a variety of challenges and with these challenges come low yields and higher costs. For example, microfluidic chips may contain sealed microstructures. They can be formed by enclosing a substrate having a pre-fabricated fluid pathway, or other microfeatures, with a thin cover plate, or with one or more additional substrates to form a three-dimensional fluid network. The pathways or other microstructures have typical dimensions in the range of micrometers to millimeters. This multilayer microfluidic structure is integrated, or joined together, by various conventional techniques. These techniques include thermal, ultrasonic, and solvent bonding. Unfortunately, these techniques often significantly alter the mated surfaces and yield distorted or completely blocked microfluidic pathways due, for example, to the low dimensional rigidity of polymeric materials under the aforementioned bonding conditions. Once the device is assembled, any blockage or obstruction in a channel is difficult or impossible to reverse. The result is that the device is lost and the manufacturing yield is lowered.
Even if the loss were acceptable, the manufacturing process is often costly because each device must be independently designed for each application. Further, each component, whether a valve, pump, or mixer, is typically specially designed for each application. To avoid designing these active features, many microfluidic systems use exterior syringe, diaphragm, or peristaltic pumps to induce fluid flow through in the microfluidic network. These systems tend to be much larger in volume than the microfluidic systems they connect to, causing problems with flow control resolution and accuracy. In the case of valves, they often have very large (on the order of 10× or more) the swept volume of the systems they are controlling. This causes great difficulty with separations, mixing, and other microfluidic functions. Companies like Upchurch Scientific (Oak Harbor, Wash.) have dedicated significant resources to the development of components that will ease the effects of these volumetric inconsistencies. However, micro pumps and valves, active components sharing the size scale and seamlessly integrated with the rest of the microfluidic system, are required.
Many of these active microfluidic components have been developed. However, very few possess the criteria necessary for integration into a complex microfluidic system. Most require very complex fabrication sequences; producing the active component is such a sensitive and intricate process that very little window is left to integrate the rest of the microfluidic system. One is left with an exquisite pump or valve with no effective way to connect or incorporate it into the microfluidic system. Often the substrates and processes are prohibitively expensive for a disposable device. Finally, the materials required to build the pump can interfere, or be incompatible with, the process the microfluidic system was intended to perform. This builds substantial non-refundable engineering costs into product development and increases the cost of the product.
In view of the foregoing, the inventors have recognized that a simple, reproducible, and high yield method for enclosing polymeric microstructures, and for forming components of these structures, particularly valve and pump systems, with easy fabrication integration is needed. Accordingly, there is a need in the art for microfluidic structures and fabrication methods that address the recognized shortcomings of the current state of technology, and which provide further benefits and advantages as those persons skilled in the art will appreciate.